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Use of Underplanting to Enhance the Health and Sustainability of Oak Dominated Ecosystems in Kentucky and the Central Hardwood Region
J. Lhotka, J. Stringer
Department of Forestry
Oak dominated forests typify the Central Hardwood Region and have both economic and biologic significance. Oak species dominate 72% of Kentucky's forests and account for nearly 50% of all hardwood timber cut in the Commonwealth. Hard mast provided by oak dominated forests is also critical to the diet of important game and non-game wildlife species. Because of market and non-market benefits oak forests provide, the perpetuation of these forests is important to Kentucky and the larger Central Hardwood Region.
Threats such as invasive forest pests, altered historical disturbance regimes, and forest decline have the potential to affect the long-term health of oak forests. To reduce the vulnerability of these forests to threats and to enhance their resiliency following disturbance, foresters must implement sustainable management strategies. Important components of these approaches would be to promote vigor in young forests through density control (thinning and release) and to enhance desirable seedling recruitment in maturing oak stands or those facing imminent attack from insects or pathogens. The proactive recruitment of oak prior to a harvest or an impending natural disturbance requires that seedlings be established under existing forest canopies. Because the presence of an existing canopy has a mitigating influence on the forest microclimate, it affects the development of oak and its competitors.
Since invasive species can alter the forest environment, land managers must also understand how these species impact forest regeneration in order to develop management solutions that perpetuate oak in the presence of diverse forest health threats. A large-scale assessment completed by Woodall, et al. (2008) suggests that current seedling and sapling densities in many mature stands are insufficient to successfully regenerate oak following disturbance.
Underplanting of nursery grown seedlings can be an effective tool for increasing advance reproduction when natural seedling densities are insufficient and is an important technique for reintroducing high value species into degraded stands. The proposed study will evaluate underplanting of tree seedlings as a method for enhancing reproduction in stands whose current conditions are not conducive to oak seedling establishment. Because understory, midstory, and overstory vegetation can alter the forest microclimate, the study will evaluate how each of these structural components affects the response of underplanted seedlings. The study will quantify the competitive effect of invasive understory vegetation on planted seedlings (Objective 1), evaluate midstory removal as a method to increase growth and survival of underplanted seedlings (Objective 2), and assess the effect of canopy gaps and residual overstory cover on seedling development (Objective 3).
Results are expected to identify components of stand structure that have the largest impact on the success of an underplanting operation. Relationships documented by this study will aid in the development of regeneration strategies to maintain oak dominated forests in Kentucky and the Central Hardwood Region.
2009 Project Description
Activities during the first year of the project included data collection and analysis of ongoing studies and the planning and layout of new research sites. Partnering with the USDA Forest Service - Southern Research Station, field work associated with the monitoring of two established underplanting studies through five growing season was completed. Data analysis and manuscript preparation was finished for the fifth year response of underplanted white oak and black oak seedlings on four intermediate quality sites in the Cumberland Plateau region. These results will be presented to researchers and forest managers at the upcoming 17th Central Hardwood Forest Conference.
Other project activities during the reporting period included the evaluation of research sites for project objectives related to the effect of invasive species on underplanted oaks and to the response of underplanted seedlings following two gap-based regeneration systems. The establishment and initial data collection for one or more of these study sites is planned for the upcoming year.
Underplanting combined with silvicultural treatments can be an effective method for establishing competitive oak seedlings when natural seedling densities are insufficient in both upland and bottomland oak forests. Unlike reliance on natural regeneration, underplanting allows managers greater control over seedling densities and species composition. Underplanting can also reintroduce high value species into degraded stands.
The study provides information regarding the response of underplanted oak seedlings to a suite of silvicultural treatments including understory competition control, midstory removal, and gap-based regeneration systems.
To date, the project has provided data on the five-year response of underplanted white and black oak seedling following midstory removal on intermediate quality sites and cherrybark oak on high quality sites. Treatments on intermediate quality sites increased diameter growth of the underplanted seedlings, but had no effect on height growth. Height growth on intermediate quality sites was considerably lower than on higher quality sites.
Planned project activities will help document the long-term response of underplanted oak seedlings and help to refine underplanting strategies for oak-dominated stands on intermediate quality sites. This work will provide information regarding the impact of species and planting stock quality on seedling growth, the efficacy of understory and midstory control, and the timing and intensity of silvicultural release treatments that follow underplanting.
Lhotka, J.M. and E.F. Loewenstein, E.F. (2009). Effect of midstory removal on understory light availability and the two-year response of underplanted cherrybark oak seedlings. Southern Journal of Applied Forestry. 33(4): 171-177.
Lhotka, J.M. and E.F. Loewenstein. 2009. A comparison of canopy structure measures for predicting height growth of underplanted seedlings. Proceedings of the 15th Biennial Southern Silvicultural Research Conference, USDA Forest Service, Southern Research Station, Asheville, NC. (In Press).
Parrott, D.L., Lhotka, J.M. , and Stringer, J.W. 2009. Effects of Midstory Removal on Underplanted Black Oak (Quercus velutina) and White Oak (Quercus alba) in Western Cumberland Plateau. Proceedings of the 17th Central Hardwood Forest Conference. (Pending).